In recent years, various kinds of portable terminals such as a cellular phone and a PC (Personal Computer) have been used. In order for these portable terminals to connect to an external network, various kinds of methods may be considered, but there is a method using a relay device called a mobile router. At one end, the mobile router connects to a base station of a cellular phone and the like connecting the external network using wide area radio, and on the other side, the mobile router connects to a wireless terminal using narrow area radio such as wireless LAN (Local Area Network). The mobile router has a relay communication function for relaying communication of a wireless terminal and a base station of a cellular phone and the like, and therefore, the portable terminal connect to an external network.
Since a mobile router is carried by a user, the mobile router is driven by the electric power provided by electric accumulation means, and the mobile router executes a relay communication. Therefore, in order to increase the operation time, it is required to suppress the electric power consumption as much as possible. However, narrow area radio such as a wireless LAN has a problem in that the electric power consumption increases. More specifically, the mobile router has a function of serving as an AP (Access Point) and transmitting beacons with a regular interval, but there is no choice but to keep on transmitting beacons as long as the mobile router functions as the AP. For this reason, this results in the increase of the electric power consumption of the mobile router (i.e., AP).
PTL 1 describes a wireless LAN device that can be used not only as a wireless base station but also as a wireless client by switching the setting of the operation mode. FIG. 10 is a schematic diagram illustrating a network system 1000 to which the wireless LAN device according to PTL 1 is applied. In the network system 1000, the Internet 1100 and a wireless LAN 1200 are connected via a router 1210. The wireless LAN 1200 includes an AP 1220 connected to the router 1210 via a LAN cable 1240, and also includes Ethernet (registered trademark) converters 1221, 1222, and 1223. The Ethernet converters 1221, 1222, and 1223 are connected to a TV (Television) receiver 1211, a PC 1212, and a printer 1213, respectively, via LAN cables 1240. The AP 1220 and the Ethernet converters 1221, 1222, and 1223 are wirelessly connected.
The AP 1220 and the Ethernet converters 1221, 1222, and 1223 have the same configuration. These can be used not only as a wireless base station (AP) but also as a wireless client (client) by switching the setting of the operation mode. These are collectively referred to as wireless LAN devices.
When one of the wireless LAN devices is turned on, a probe request packet is transmitted to another wireless LAN device. The another wireless LAN device which is the destination of transmission of the probe request packet transmits a probe response as a response to the probe request packet to the one wireless LAN device. When the one wireless LAN device receives the probe response, the one wireless LAN device (i.e., a device in question) is activated as a wireless client (client). The wireless client does not transmit any beacon, and therefore, the electric power consumption can be reduced when it is activated as a wireless client (client).